U.S. patent application number 13/297441 was filed with the patent office on 2013-05-16 for glass ceramics for use as a dielectric for gigahertz applications.
This patent application is currently assigned to SCHOTT AG. The applicant listed for this patent is Bernd Hoppe, Michael Kluge, Stephan Knoener, Martin Letz, Bernd Ruedinger, Daniela Seiler. Invention is credited to Bernd Hoppe, Michael Kluge, Stephan Knoener, Martin Letz, Bernd Ruedinger, Daniela Seiler.
Application Number | 20130120193 13/297441 |
Document ID | / |
Family ID | 48280061 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130120193 |
Kind Code |
A1 |
Hoppe; Bernd ; et
al. |
May 16, 2013 |
GLASS CERAMICS FOR USE AS A DIELECTRIC FOR GIGAHERTZ
APPLICATIONS
Abstract
A glass-ceramic which is particularly suitable as dielectric for
use in the high-frequency range, in particular as dielectric
resonator, as electronic frequency filter element or as antenna
element is disclosed. The glass-ceramic has at least the following
constituents (in mol % on an oxide basis): 5-50% of SiO.sub.2,
0-20% of Al.sub.2O.sub.3, 0-25% of B.sub.2O.sub.3, 0-25% of BaO,
10-60% of TiO.sub.2, 5-35% of Re.sub.2O.sub.3, where Ba can be
partly replaced by Sr, Ca, Mg, where Re is a lanthanide or yttrium
and where Ti can be partly replaced by Zr, Hf, Y, Nb, V, Ta.
Inventors: |
Hoppe; Bernd; (Ingelheim,
DE) ; Kluge; Michael; (Offenbach A. M., DE) ;
Knoener; Stephan; (Herford, DE) ; Letz; Martin;
(Mainz, DE) ; Ruedinger; Bernd; (Woerrstadt,
DE) ; Seiler; Daniela; (Alzey, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hoppe; Bernd
Kluge; Michael
Knoener; Stephan
Letz; Martin
Ruedinger; Bernd
Seiler; Daniela |
Ingelheim
Offenbach A. M.
Herford
Mainz
Woerrstadt
Alzey |
|
DE
DE
DE
DE
DE
DE |
|
|
Assignee: |
SCHOTT AG
Mainz
DE
|
Family ID: |
48280061 |
Appl. No.: |
13/297441 |
Filed: |
November 16, 2011 |
Current U.S.
Class: |
343/700MS ;
501/32; 65/33.7 |
Current CPC
Class: |
C03C 3/068 20130101;
C03C 10/0054 20130101; H01Q 9/0407 20130101; C03C 4/16 20130101;
C03C 10/0036 20130101 |
Class at
Publication: |
343/700MS ;
501/32; 65/33.7 |
International
Class: |
C03C 10/00 20060101
C03C010/00; H01Q 9/04 20060101 H01Q009/04 |
Claims
1. A glass-ceramic which has at least the following constituents
(in mol % on an oxide basis): TABLE-US-00006 SiO.sub.2 5-50
Al.sub.2O.sub.3 0-20 B.sub.2O.sub.3 0-25 BaO 0-25 TiO.sub.2 10-60
RE.sub.2O.sub.3 5-35,
where Ba can be partly replaced by at least one element selected
from the group consisting of Sr, Ca and Mg; where RE is selected
from the group consisting of at least one lanthanide and yttrium;
and where Ti can be partly replaced by at least one element
selected from the group consisting of Zr, Hf, Y, Nb, V and Ta.
2. The glass-ceramic according to claim 1 which has the following
constituents (in mol % on an oxide basis): TABLE-US-00007 SiO.sub.2
10-40 Al.sub.2O.sub.3 0-10 B.sub.2O.sub.3 5-25 BaO 0-20 TiO.sub.2
15-50 RE.sub.2O.sub.3 10-30,
where Ba can be partly replaced by at least one element selected
from the group consisting of Sr, Ca and Mg; where RE is selected
from the group consisting of at least one lanthanide and yttrium;
and where Ti can be partly replaced by at least one element
selected from the group consisting of Zr, Hf, Y, Nb, V and Ta.
3. The glass-ceramic according to claim 1, in which up to 10% of
the barium is replaced.
4. The glass-ceramic according to claim 1, in which up to 10% of
the titanium is replaced.
5. The glass-ceramic according to claim 1, which additionally
contains from 0.01 to 3 mol % of at least one refining agent.
6. The glass-ceramic according to claim 5, in which the at least
one refining agent is selected from the group consisting of
Sb.sub.2O.sub.3 and As.sub.2O.sub.3.
7. The glass-ceramic according to claim 1, which has a dielectric
loss (tan .delta.) of not more than 10.sup.-2 in the high-frequency
range (frequency f>200 MHz).
8. The glass-ceramic according to claim 1, having a relative
permittivity .di-elect cons. of at least 15.
9. The glass-ceramic according to claim 1, wherein the absolute
value of the temperature dependence of the resonance frequency
|.tau..sub.f| is not more than 200 ppm/IC.
10. The glass-ceramic according to claim 1, wherein the absolute
value of the temperature dependence of the resonance frequency
|.tau..sub.f| is not more than 10 ppm/K.
11. The glass-ceramic according to claim 1, which contains at least
one mixed crystal phase based on RE, Ti, Si, O, Ba, where Ba can be
at least partly replaced by Sr, Ca, Mg, where RE is a lanthanide or
yttrium and where Ti can be at least partly replaced by Zr, Hf, Y,
Nb, V, Ta.
12. The glass-ceramic according to claim 1, which contains at least
one mixed crystal phase selected from the group consisting of
BaRETiO, RE.sub.2Ti.sub.2O.sub.7, RE.sub.2Ti.sub.2SiO.sub.9 and
RE.sub.4Ti.sub.9O.sub.24, where RE lanthanum, another lanthanide or
yttrium, where up to 10% of Ba can be replaced by Sr, Ca, Mg and
where up to 10% of Ti can be replaced by Zr, Hf, Y, Nb, V, Ta.
13. The glass-ceramic according to claim 1, which has a proportion
of crystalline material of at least 30% by volume.
14. The glass-ceramic according to claim 13, which has a proportion
of crystalline material of up to 95% by volume.
15. The glass-ceramic according to claim 1, having an average
crystallite size of from 10 nanometres to 50 microns.
16. An antenna element for the high-frequency range which has a
glass-ceramic according to claim 1 which is partly metallized on
the outer surface thereof.
17. The antenna element according to claim 16, which is formed as
an antenna selected from the group consisting of a cylindrical
antenna element and a patch antenna element.
18. A method of producing a dielectric having a dielectric loss of
not more than 10.sup.-2 in the high-frequency range, comprising the
following steps: melting and homogenizing a starting glass
containing the constituents (in mol % on an oxide basis):
TABLE-US-00008 SiO.sub.2 5-50 Al.sub.2O.sub.3 0-20 B.sub.2O.sub.3
0-25 BaO 0-25 TiO.sub.2 10-60 RE.sub.2O.sub.3 5-35,
where Ba can be partly replaced by at least one element selected
from the group consisting of Sr, Ca and Mg; where RE is selected
from the group consisting of at least one lanthanide and yttrium;
and where Ti can be partly replaced by at least one element
selected from the group consisting of Zr, Hf, Y, Nb, V and Ta;
pouring the starting glass into a desired mould; cooling the
starting glass to room temperature; ceramizing the starting glass
by means of a heat treatment.
19. The method of claim 18, in which the starting glass has at
least the following constituents (in mol % on an oxide basis):
TABLE-US-00009 SiO.sub.2 10-40 Al.sub.2O.sub.3 0-10 B.sub.2O.sub.3
5-25 BaO 0-20 TiO.sub.2 15-50 RE.sub.2O.sub.3 10-30,
where Ba can be partly replaced by at least one element selected
from the group consisting of Sr, Ca and Mg; where RE is selected
from the group consisting of at least one lanthanide and yttrium;
and where Ti can be partly replaced by at least one element
selected from the group consisting of Zr, Hf, Y, Nb, V and Ta.
20. The method of claim 19, in which the starting glass is brought
to near net shape by means of a melt-technological process.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a glass-ceramic which can be used
as dielectric in the high-frequency range (frequency>200 MHz),
in particular in the gigahertz range (frequency f>1 GHz).
[0002] Special materials which have a very high relative
permittivity .di-elect cons. combined with a very low dielectric
loss (tan .delta.) are required for a number of applications in the
high-frequency range. To avoid close-range detuning due to the body
of a user (referred to as "body loading"), dielectric charging of
antennae, filters and other devices is of particular importance.
This requires dielectrics which have a high relative permittivity,
with .di-elect cons.>15, and a low dielectric loss (tan .delta.)
of not more than 10.sup.-2, preferably lower, in the high-frequency
range. Furthermore, the temperature dependence of the resonance
frequency .tau..sub.f should be very small. Finally, such a
material should be able to be processed in a very simple and
inexpensive way in order to make near net shapes possible at low
cost.
[0003] A number of ceramic materials which are processed by
sintering processes are known in the prior art. These include a
BiNbO.sub.4 system which has been disclosed in Mirsaneh et al.,
"Circularly Loaded Dielectric-Loaded Antennas: Current Technology
and Future Challenges", Adv. Funct. Materials 18, (2008), pp. 1-8,
for use in the case of dielectrically charged antennae for the
gigahertz range. This material is used for producing the two most
widely used forms of antennae, the circularly polarized DLA helix
antenna (D-LQH antenna) and the square patch antenna. For this
purpose, a glass having the composition 30 mol % of
Bi.sub.2O.sub.3, 30 mol % of Nb.sub.2O.sub.5, 30 mol % of
B.sub.2O.sub.3 and 10 mol % of SiO.sub.2 is melted in a
conventional way at 1250.degree. C. for two hours.
[0004] This glass was poured into cylindrical moulds, depressurized
at from 500 to 520.degree. C. and slowly cooled to room
temperature. Crystallization was subsequently carried out at
various temperatures in the range from 600.degree. C. to
1000.degree. C. The optimal value for antennae applications is said
to be, for a heat treatment at 960.degree. C., a relative
permittivity .di-elect cons. of 15 with a quality factor Qf.sub.0
of 15 000 GHz and a temperature coefficient of the resonance
frequency .tau..sub.r of -80 MK.sup.-1. The crystalline phase
determined here was essentially orthorhombic BiNbO.sub.4.
[0005] This system using bismuth and niobium is very expensive in
terms of the raw materials.
[0006] In addition, there are a number of sintered ceramic
materials (cf. U.S. Pat. No. 6,184,845 B1, US 2007/063902 A1). In
these references, a sintered ceramic material based on zirconium
titanate or based on zirconium-tin titanate having a relative
permittivity of about 36 is disclosed as dielectric material for
the ceramic core of a dielectrically charged D-LQH antenna. The
material is said to be produced by extrusion or pressing and
subsequent sintering.
[0007] Further sintered materials are indicated in the review by M.
T. Sebastian et al., "Low loss dielectric materials for LTCC
applications", International Materials Reviews, Vol. 53, 2008, pp.
57-90. Even though some of these materials are referred to as
"glass-ceramics", they are sintered materials since they are
produced by sintering a mixture of vitreous and crystalline
powders.
[0008] Dielectrics produced by sintering have a number of
disadvantages: every sintering process is always accompanied by a
certain shrinkage, which leads to geometric inaccuracies and
corresponding final machining. Furthermore, every sintering process
results in a certain residual porosity which is a disadvantage when
the surface is metalized. The metal penetrates into the pores and
increases the dielectric loss of the dielectric.
[0009] In addition, the production of sintered materials is
fundamentally relatively complicated and expensive.
SUMMARY OF THE INVENTION
[0010] A first object of the invention is to provide an improved
material which can be used as dielectric for high-frequency
applications.
[0011] A second object of the invention is to provide an improved
material which has a high relative permittivity.
[0012] A third object of the invention is to provide an improved
material which has a low dielectric loss.
[0013] A fourth object of the invention is to provide an improved
material for a dielectric, which should be able to be produced and
processed in a very simple and inexpensive way.
[0014] A fifth object of the invention is to provide an improved
antenna element which can be used in particular in a dielectrically
charged antenna which can be reduced using a body loading.
[0015] According to the invention, these and other objects are
achieved by a glass-ceramic which has at least the following
constituents (in mol % on an oxide basis):
TABLE-US-00001 SiO.sub.2 5-50 Al.sub.2O.sub.3 0-20 B.sub.2O.sub.3
0-25 BaO 0-25 TiO.sub.2 10-60 RE.sub.2O.sub.3 5-35,
[0016] where Ba can be partly, preferably to an extent of up to
10%, replaced by Sr, Ca, Mg, where RE is lanthanum, another
lanthanide or yttrium, and Ti can be partly, preferably to an
extent of up to 10%, replaced by Zr, Hf, Y, Nb, V, Ta.
[0017] The object of the invention is solved completely in this
way.
[0018] It has been found that homogeneous glasses which can
subsequently be converted by a ceramicizing treatment into a
homogeneous glass-ceramic which has a high relative permittivity, a
low dielectric loss and a low temperature dependence of the
resonance frequency can be melted using such a glass composition.
The material can be produced as glass ceramic in a simple and
inexpensive way and allows near net shaping by melt-technological
processes, in particular by casting or optionally by pressing.
[0019] For the purposes of the present patent application, the term
"glass-ceramic" refers to a material which, starting from a
homogeneous glass produced by melting, is converted by means of a
specific heat treatment into a partially crystalline body in which
a large number of crystallites are distributed essentially
homogeneously in a vitreous residual phase.
[0020] In an advantageous embodiment of the invention, the
glass-ceramic has the following constituents (in mol % on an oxide
basis):
TABLE-US-00002 SiO.sub.2 10-40 Al.sub.2O.sub.3 0-10 B.sub.2O.sub.3
5-25 BaO 0-20 TiO.sub.2 15-50 Re.sub.2O.sub.3 10-30,
[0021] where Ba can be partly, preferably to an extent of up to
10%, replaced by Sr, Ca, Mg, where Re is a lanthanide or yttrium,
and Ti can be partly, preferably to an extent of up to 10%,
replaced by Zr, Hf, Y, Nb, V, Ta.
[0022] Furthermore, the glass-ceramic can contain refining agents
in customary amounts, preferably from 0.01 to 3 mol % of a refining
agent which is preferably selected from the group consisting of
Sb.sub.2O.sub.3 and As.sub.2O.sub.3.
[0023] The glass-ceramic of the invention preferably has a
dielectric loss (tan .delta.) of not more than 10.sup.-2,
preferably not more than 10.sup.-3, in high-frequency applications
(f>200 MHz).
[0024] Furthermore, the glass-ceramic preferably has a relative
permittivity .di-elect cons. of at least 15, preferably >18,
preferably in the range from 20 to 80.
[0025] The glass-ceramic of the invention also preferably has a
temperature dependence of the resonance frequency .tau..sub.f of
not more than 200 ppm/K, preferably not more than 50 ppm/K,
particularly preferably not more than 10 ppm/K.
[0026] In a further advantageous embodiment of the invention, the
glass-ceramic of the invention has at least one mixed crystal phase
based on RE, Ti, Si, O and optionally Ba, where Ba can be at least
partly, replaced by Sr, Ca, Mg, where RE is a lanthanide or
yttrium, and Ti can be at least partly replaced by Zr, Hf, Y, Nb,
V, Ta.
[0027] In particular, the glass-ceramic of the invention can
contain at least one mixed crystal phase selected from the group
consisting of Ba, RE, TiO, RE.sub.2Ti.sub.2O.sub.7,
RE.sub.2Ti.sub.2SiO.sub.9 and RE.sub.4Ti.sub.9O.sub.24, where RE is
lanthanum, another lanthanide or yttrium, up to 10% of Ba can be
replaced by Sr, Ca, Mg, and up to 10% of Ti can be replaced by Zr,
Hf, Y, Nb, V, Ta.
[0028] The glass-ceramic of the invention can preferably have a
proportion of crystalline material of at least 30% by volume,
preferably up to 95% by volume.
[0029] The average crystallite size is preferably from 10 nm to 50
.mu.m and is preferably in the range from 100 nm to 1 .mu.m.
[0030] The glass-ceramic of the invention is particularly suitable
as dielectric for a dielectric resonator, an electronic frequency
filter element or an antenna element in the high-frequency range
(f>200 MHz).
[0031] Use as dielectric for a cylindrical antenna element or a
patch antenna element is particularly useful.
[0032] A dielectric according to the invention having a dielectric
loss of not more than 10.sup.-2 in the high-frequency range can be
produced by means of the following steps:
[0033] melting and homogenization of a starting glass containing
the constituents (in mol % on an oxide basis):
TABLE-US-00003 SiO.sub.2 5-50 Al.sub.2O.sub.3 0-20 B.sub.2O.sub.3
0-25 BaO 0-25 TiO.sub.2 10-60 RE.sub.2O.sub.3 5-35,
[0034] where Ba can be partly, preferably to an extent of up to
10%, replaced by Sr, Ca, Mg, where RE is a lanthanide or yttrium,
and Ti can be partly, preferably to an extent of up to 10%,
replaced by Zr, Hf, Y, Nb, V, Ta;
[0035] pouring of the starting glass into a desired mould;
[0036] cooling of the starting glass to room temperature;
[0037] ceramicization of the starting glass by means of a heat
treatment.
[0038] In a preferred embodiment of the invention, the starting
glass comprises at least the following constituents (in mol % on an
oxide basis):
TABLE-US-00004 SiO.sub.2 10-40 Al.sub.2O.sub.3 0-10 B.sub.2O.sub.3
5-25 BaO 0-20 TiO.sub.2 15-50 RE.sub.2O.sub.3 10-30,
[0039] where Ba can be partly, preferably to an extent of up to
10%, replaced by Sr, Ca, Mg, where RE is a lanthanide or yttrium,
and Ti can be partly, preferably to an extent of up to 10%,
replaced by Zr, Hf, Y, Nb, V, Ta.
[0040] The starting glass is preferably brought to near net shape
by means of a hot forming process, in particular by casting, tube
drawing, rod drawing or extrusion.
[0041] Further features and advantages of the invention can be
derived from the following description of preferred examples with
reference to the drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0042] FIG. 1, the only FIGURE, shows the result of an X-ray
diffraction analysis.
DESCRIPTION OF PREFERRED EMBODIMENTS
Examples
[0043] Table 1 shows various glass compositions for a starting
glass in the system Ba--La--Ti--Si--O.
[0044] The various glass samples of Examples 1 to 9 are firstly
melted and homogenized in the usual way using conventional starting
materials, with platinum crucibles, PT/RI crucibles, PT/RH
crucibles, fused silica crucibles or aluminium oxide crucibles
being able to be used. The samples are firstly melted at
1350.degree. C. for 2 hours, then refined at 1400.degree. C. for 30
minutes, stirred and homogenized by means of a platinum stirrer for
20 minutes, allowed to stand for 10 minutes and then poured into
suitable moulds made of, for instance, steel, graphite, aluminium
oxide or fused silica and then brought to near net shape.
[0045] After cooling to room temperature, the glass is subjected to
a ceramicization step, which can be carried out, for example, by
means of an infrared heating process or by means of a conventional
process.
[0046] A typical ceramicization cycle by means of an infrared
furnace is as follows:
[0047] heating at 300.degree. C./min to 1050.degree. C.;
[0048] hold at 1050.degree. C. for 7 seconds;
[0049] heating to 1200.degree. C. at a heating rate of 50
K/min;
[0050] hold at 1200.degree. C. for 15 minutes;
[0051] cooling to about 500.degree. C. at a cooling rate of about
50 K/min by switching off the furnace;
[0052] removal of the specimen from the furnace when a temperature
of about 500.degree. C. has been reached.
[0053] A ceramicization cycle in a conventional furnace is carried
out by heat treatment at 925.degree. C. for 15 hours.
[0054] If necessary, the mouldings can, after casting, be subjected
to a file grinding or polishing treatment or in the case of the
production of cylindrical mouldings, can be machined by centreless
grinding of the cylindrical surface.
[0055] FIG. 1 shows an X-ray diffraction analysis of sample 9 after
ceramicization. The clearly predominant crystal phase is
La.sub.2Ti.sub.2SiO.sub.9. In addition, small proportions of rutile
TiO.sub.2 were found.
[0056] The proportion by volume of the crystalline phase in this
sample is in the order of from about 50 to 70% by volume.
[0057] Relative permittivities .di-elect cons. were measured on
samples 1 to 9; these were all greater than 15 and in the range
from 20 to 50,
[0058] The samples also display a low dielectric loss and a high
quality.
[0059] The quality Q is the reciprocal of the dielectric loss (tan
.delta.):
Q=1/tan(.delta.)
[0060] The quality is measured by the Hakki-Coleman resonance
method. The quality factor is determined here as the product of
quality Q and measurement frequency f.sub.0.
[0061] All samples 1 to 9 had a quality factor Qf.sub.0 in the
range from 2000 to 3000 GHz. In the case of sample 1, a relative
permittivity .di-elect cons. of 22.4 and a quality Q of 205 were
measured at 10.09 GHz, i.e. a quality factor of 2068 was
measured.
[0062] The temperature coefficient .SIGMA..sub.f of the resonance
frequency is very low for all measured samples and is in the range
-40 ppm/K<.tau..sub.f<40 ppm/K.
[0063] In uses as dielectric for antennae which are suitable, in
particular, for mobile GPS antennae for mobile phones, the
frequency range is above 200 MHz, in particular in the range from
about 800 MHz to 70 GHz. The dielectric charging of the antenna
reduces the sensitivity of the antenna to detuning by the user.
TABLE-US-00005 TABLE 1 Sample number 1 2 3 4 5 6 7 8 9 Content
Content Content Content Content Content Content Content Content
Component in mol % in mol % in mol % in mol % in mol % in mol % in
mol % in mol % in mol % SiO.sub.2 21.00 23.00 27.00 19.00 23.00
19.00 27.00 21.00 21.00 Al.sub.2O.sub.3 6.00 4.00 2.00 2.00 2.00
4.00 2.00 4.00 6.00 B.sub.2O.sub.3 12.60 10.50 10.50 14.50 12.50
12.50 10.50 10.50 12.60 BaO 0.00 14.75 14.25 15.25 14.75 15.25
14.25 15.25 0.00 TiO.sub.2 40.20 34.90 33.90 35.90 34.90 35.90
33.90 35.90 40.20 Sb.sub.2O.sub.3 0.10 0.10 0.10 0.10 0.10 0.10
0.10 0.10 0.10 La.sub.2O.sub.3 20.10 12.75 12.25 13.25 12.75 13.25
12.25 13.25 20.10 Total 100.00 100.00 100.00 100.00 100.00 100.00
100.00 100.00 100.00
* * * * *